The present invention pertains to the art of conveyor chains and, more particularly, to relatively long single strand roller chain conveyors which utilize long extended chain connecting pins on which articles being conveyed are carried or attached.
Such conveyors are well known in the art and are used, for example, in the coating of beverage cans and, in particular, to convey the cans through painting and/or coating equipment and into and through a baking or curing oven wherein the drying of painted or laquered surfaces of the cans is speeded. The chains in these conveyors are generally disposed in a vertically oriented serpentine path with the extended chain pins horizontally disposed. The cans or other articles being conveyed are simply placed open-end-first horizontally onto the extended pins and carried along the serpentine course through the coaters and the oven or drying area. The chain used in such conveyors is generally a standard roller chain, with a No. 60 roller chain having a 3/4 inch chain pitch (distance between link connecting pins) being typical.
To provide the can conveying attachments on these roller chains, selected standard link connecting pins are replaced with long extended chain pins. These extended chain pins thus function both to interconnect the chain links and to carry the cans. In a conveyor designed to carry standard size beverage cans, the spacing of the extended length chain connecting pins may be every six or seven chain pitches or, in a typical No. 60 roller chain, every 41/2 to 51/4 inches. A typical coating and drying operation will require a conveyor length of from 500 to 800 feet and, thus, from approximately 1000 to over 2000 extended pins for conveying cans. The extended pins, which typically extend about 7 inches outwardly of the chain, must be strong and quite rigid in order to avoid vibration or deflection of the pins which would tend to dislodge the cans. Since a No. 60 roller chain has link connecting pins of approximately 1/4 inch diameter, the extended length pins (which must also serve as connecting pins) are conveniently of the same diameter and provide the required strength and rigidity.
Over the course of a coating and drying conveyor, and particularly in the serpentine drying portion which comprises the greater portion of the total conveyor length, there are numerous tracking, guiding and supporting structures with relatively small clearances for the moving conveyor chain and attached cans. Frequent slight displacement of the cans on the extended chain pins occurs and snags or jams of the pins and/or cans on the various structures is commonplace and unavoidable. As a result, pin breakage or severe bending frequently occurs and, although a small number of broken pins may be tolerated with little inconvenience, broken pins must eventually be replaced and bent pins may so interfere with conveyor operation that immediate replacement is required. In either case, the conveyor must be stopped and the entire chain disconnected, often in many places. This is both costly and extremely time consuming.
In one prior art attempt to solve this problem, the extended chain pins are notched or grooved at a point outward of the chain links. The notch or groove provides a weakened area in the pin allowing the extended pin to break away if an obstruction is encountered. This controlled break away has helped to solve the problem of bent pins, but has done nothing to resolve the more serious problem of costly connecting pin replacement.
Further, customer needs at times require the use of special materials for the extended chain pins, either for compatibility with the articles being conveyed or because of the environment in which the chain operates. For example, stainless steel pins are often required for carrying cans through the coating and drying operations, however, stainless steel is a poor substitute for plain carburized steel normally used for roller chain connecting pins and the wear life of the chain is adversely affected if stainless steel extended chain pins are used.
Also in some application wherein cans are automatically inserted onto the conveyor chain onto every extended pin if such pin were broken off--missing then the can would be inserted and would fall down and oftentime result in jam-ups plus product loss.